1. Field of the Invention
The present invention relates to a method of formation of an impeller which is used in a compressor and blower etc. and to an impeller which is formed by such a method.
2. Description of the Related Art
In a compressor and blower etc., an impeller with a plurality of blades attached to a hub is used. In general, these blades are expressed by connecting curves which extend along a hub surface and curves which extend along a shroud surface by a plurality of straight lines.
FIG. 7A is a perspective view of an impeller for explaining a general technique for expressing a blade. To facilitate understanding, FIG. 7A shows only a single blade 4.
First, a curve 2 which extends along the hub surface and a curve 1 which extends along the shroud surface are defined. Then, each of these curves 1, 2 is divided into a predetermined number of equal intervals. After that, the divided locations of the curves 1, 2 are connected by a plurality of straight lines 3. Due to this, a blade 4 is formed (see FIG. 7B which is a view along the meridian of the blade which is shown in FIG. 7A).
By employing such a technique, it is possible to simply form a blade. Further, Japanese Patent Publication No. 8-254198A, FIG. 6, and Japanese Utility Model Publication No. 4-54997U, FIG. 3, show similarly formed blades.
In this regard, as can be seen from FIG. 7B, when using the above technique to express a blade, the curve 2 which extends along the hub surface is longer than the curve 1 which extends along the shroud surface. In this regard, FIG. 7C is a cross-sectional view of the impeller in the plane A of FIG. 7A. The plane A extends in the vertical direction with respect to the axis of the hub 5. As shown in FIG. 7C, the cross-section of the blade 4 is for example curved in the counter clockwise direction.
However, when a blade with a cross-section of a substantially straight shape is required, a blade with a cross-section of a curved shape does not satisfy the required performance. In such a case, it is necessary to again redefine the curve 2 which extends along the hub surface and the curve 1 which extends along the shroud surface. Such work is complicated and requires tremendous time.
The present invention was made in consideration of such a situation and has as its object the provision of a method of formation of an impeller which enables the easy formation of a high performance impeller which is provided with a blade with a cross-section of a substantially straight shape and an impeller which is formed by such a method.